Radio trunked communication systems are known in the art and typically comprise a communication resource controller operably coupled to a predetermined number of communication resources that provide communications to a plurality of communication units. Typically, one of the communication resources is used as a control communication resource, while the other communication resources are used as working communication resources. In most of these systems, the control communication resource is dedicated to only communicate control information between the communication resource controller and the plurality of communication units. A working communication resource is typically used to communicate information such as voice or data between communication units. Two well known techniques that utilize a dedicated control communication resource are commonly known as message trunking and transmission trunking.
With message trunking, a working communication resource is assigned for use for a time greater than that of a single transmission. Thus, a working communication resource, once assigned, is retained for multiple transmissions of a message.
With transmission trunking, a working communication resource is assigned for use for a single transmission only. Subsequent transmissions of the message require new assignments of working communication resource(s), even if the same working communication resource is assigned for a subsequent transmission of the message.
In both of these techniques, when a single communication unit from amongst the plurality of communication units wishes to communicate, the communication unit transmits, on the control communication resource, a communication resource allocation request to the communication resource controller. Upon receiving the communication resource allocation request, and subsequently determining the availability of a working communication resource, the communication resource controller transmits a communication resource assignment of the working communication resource to the communication unit on the control communication resource. The communication unit then affiliates with the working communication resource and makes a first transmission.
With message trunking, when the communication unit completes the first transmission, the working communication resource assignment remains unchanged for a predetermined period of time commonly known as drop-out time. The drop-out time is the time during which a second transmission of this message may begin on the working communication resource. The drop-out time is re-initialized after each transmission, hence, once the working communication resource is assigned, a plurality of transmissions may be made on the working communication resource without utilizing the control communication resource. If the drop-out time expires before a transmission is made, the communication unit returns to the control communication resource and the working communication resource becomes available for re-assignment. To make a transmission after the drop-out time expires, the communication unit must repeat the process of communicating with the communication resource controller to have an available working communication resource assigned, as described above. This method allows efficient use of the control communication resource because a single transmission of a communication resource assignment on the control communication resource allows a plurality of transmissions on a working communication resource. Such a method does not, however, use the working communication resources efficiently as an assigned working communication resource cannot be re-assigned until the drop-out time expires.
With the transmission trunking technique, when the communication unit completes the first transmission on the assigned working communication resource, the communication unit returns to the control communication resource and the working communication resource becomes available for re-assignment almost immediately. Each subsequent transmission requires the steps of transmitting a communication resource allocation request and receiving a communication resource assignment of a working communication resource on the control communication resource, and then affiliating with the working communication resource, as described earlier, before the subsequent transmission may be made. Hence, each transmission utilizes the control communication resource as well as the working communication resource. This method allows efficient use of the working communication resources, as working communication resources are assigned only for the duration of a transmission. Such a method, however, generates a significant amount of traffic on the control communication resource, which in turn limits the number of working communication resources, and hence the number of communication units, that may be supported by the communication resource controller.
Accordingly, a need exists for a method of transmitting messages that utilizes the control communication resource and the working communication resources efficiently.